Touch sensing systems (“touch systems”) are in widespread use in a variety of applications. Typically, the touch systems are actuated by a touch object such as a finger or stylus, either in direct contact, or through proximity (i.e. without contact), with a touch surface. Touch systems are for example used as touch pads of laptop computers, in control panels, and as overlays to displays on e.g. hand held devices, such as mobile telephones. A touch panel that is overlaid on or integrated in a display is also denoted a “touch screen”. Many other applications are known in the art. To an increasing extent, touch systems are designed to be able to detect two or more touches simultaneously, this capability often being referred to as “multi-touch” in the art.
There are numerous known techniques for providing multi-touch sensitivity, e.g. by using cameras to capture light scattered off the point(s) of touch on a touch panel, or by incorporating resistive wire grids, capacitive sensors, strain gauges, etc into a touch panel.
WO2011/028169 and WO2011/049512 disclose multi-touch systems that are based on frustrated total internal reflection (FTIR). Light sheets are coupled into a panel to propagate inside the panel by total internal reflection (TIR). When an object comes into contact with a touch surface of the panel, the propagating light is attenuated at the point of touch. The transmitted light is measured at a plurality of outcoupling points by one or more light sensors. The signals from the light sensors are processed for input into an image reconstruction algorithm that generates a 2D representation of interaction across the touch surface. This enables repeated determination of current position/size/shape of touches in the 2D representation while one or more users interact with the touch surface. Examples of such touch systems are found in U.S. Pat. No. 3,673,327, U.S. Pat. No. 4,254,333, U.S. Pat. No. 6,972,753, US2004/0252091, US2006/0114237, US2007/0075648, WO2009/048365, US2009/0153519, WO2010/006882, WO2010/064983, and WO2010/134865.
An overall goal for the touch system is to consume less energy to save resources and reduce costs. For example, when the system is not used it can be in a power saving mode or an idle mode in which modes the system is configured to use less power than in a normal mode. Such a system is disclosed in e.g. WO2011/028170 which uses a less number of emitters/detectors in power saving or idle mode than in a normal detect mode to save power. When an interaction on the touch surface is detected, the system is turned into normal mode.
The touch technology is now being implemented into consumer products such as smartphones and laptops. These products commonly have a limited access to power, e.g. battery, and new challenges are approached when integrating the touch system into the often smaller products. An ASIC (Application Specific Integrated Circuit) has been developed to which a limited number of emitters and detectors are connected. By using ASICs the touch system can be made smaller and use less energy. The whole touch system comprises a plurality of ASIC blocks with connected emitters and detectors.
The need for power saving solutions is however still present. The system needs to monitor when to change mode from a power saving or idle mode to a normal mode and this monitoring uses power. A common used approached is to have a button to activate the touch system. A mechanical part is thus sensitive to mechanical failure.
From US2012/0191993 a system and method is known for reducing power consumption in an electronic device such as a mobile phone having a touch-sensitive display. The system comprises a touch panel controller, which may have resource constraints compared to a main processor, for preliminary gesture recognition to transition the electronic device from sleep mode to full power mode. The touch panel controller consumes less power than the main processor and power can thus be saved.
It is an object of the present invention to provide a low power function which takes advantage of a distributed control structure of the touch system.